1. Field of the Invention
The present invention relates to a method for removing contaminants from integrated circuit devices. The invention relates more particularly to a method for removing alkali metal (e.g., sodium, potassium, etc.) and halogen-based (e.g., fluorine) contaminants from the surfaces of an integrated circuit as the device is being fabricated.
2. Background of the Invention
Semiconductor integrated circuit devices typically comprise multiple layers of vertically stacked metal interconnect layers with dielectric materials disposed between them. The fabrication of such devices typically involves the repeated deposition or growth, patterning, and etching of thin films of semiconductor, metal, and dielectric materials. Between these process steps the device is typically subjected to various cleaning steps which involve cleaning surface contaminants and residues, removal of damaged surface layers, and chemical conditioning of the material surface to optimize subsequent processing. Such etching and cleaning steps result in undesirable materials being present on the surface of the device as it is being fabricated.
For example, it is known to form a patterned resist layer, such as an oxide hard mask or polymeric resist, on a metal-containing layer (which is usually formed by a deposition process) using conventional photoresist and photolithographic techniques. After the oxide hard mask or polymeric resist is formed, conventional reactive ion etching processes using halogen-containing etchants, such as Cl.sub.2, BCl.sub.3, CCl.sub.4, SiCl.sub.4, CF.sub.4, NF.sub.3, SF.sub.6, and mixtures thereof, are used to etch the metal-containing layers to form a patterned metal-containing layer. Such reactive etching processes leave corrosive etchant byproducts, remnant resist, and sidewall deposits on the sidewalls of the etched features.
Moreover, it is typical to then cover the patterned metal-containing layer with a suitable dielectric material, such as silicon oxide, silicon nitride, or any other film that has dielectric properties. The dielectric layer is then, typically, masked and etched to open narrow profile openings in the dielectric layer. Such openings are known as vias and serve to provide a point of contact between the underlying metal-containing layer and a metal-containing layer subsequently applied over the dielectric material. Vias are typically formed by a plasma etching process which is well known to those of skill in the art. It is typical for the vias to be defined by placing a photoresist pattern over the dielectric layer and then etching the exposed dielectric layer to form the vias. For example, the dielectric film may be etched in a plasma processing reactor utilizing a fluorine based gas such as CHF.sub.3, CF.sub.4, C.sub.2 F.sub.6, sometimes in combination with O.sub.2, Ar or He. A typical process for etching a dielectric layer to form a via is described in U.S. Pat. No. 5,176,790, which issued in the names of Arleo et al., the subject matter of which is herein incorporated by reference.
Unfortunately, since etching of the metal-containing layer is normally accomplished utilizing a halogen-based gas (e.g., chlorine) the etching process results in contamination of the device with, among other things, a halogen such as chlorine. When the chlorine contaminant is exposed to moisture, corrosion of the device results. Moreover, etching of the dielectric layer is typically conducted within a chamber, by utilizing a halogen-based (e.g., fluorine) plasma. To withstand the harsh conditions generated by the halogen-based (e.g., fluorine) plasma, the components within the chamber are normally fabricated from ceramic materials, with alumina being a preferred ceramic material for such chamber components. However, the ceramic components, when subjected to the plasma conditions, tend to contaminate the device with alkali metal (e.g., potassium, sodium, etc.).
Such halogen and alkali contaminants must be removed to obtain optimum performance, since the contaminants may lead to device defects, lower oxide breakdown fields, and corrosion problems as well.
It is known to follow the etching steps with a post-etch rinse, which, typically, comprises using an organic solvent. Such post-etch rinses are utilized to remove organic residues, inorganic residues, or mixed organic-inorganic residues. The composition of the post-etch rinse organic solvent will depend, of course, on the residue being removed.
A problem associated with the exposure of the metal films, dielectric materials and polymeric resist materials to organic solvents is that the solvents frequently have the detrimental consequences of metal corrosion, redeposition of contaminants and metallic contamination. A particular problem is that the surfaces may adsorb metallic ions, such as from alkali metals in the organic solvents. Particularly, metallic and dielectric films are vulnerable to contamination by alkali metals contained in the organic solvents.
Thus, it has been proposed to remove such contaminants by utilizing a down stream halogen-based (e.g., fluorine) plasma etch to etch a thin layer of the contaminated device surface (i.e., the dielectric surface, metal-containing layer surface, via wall surface, etc.). The device is then subsequently rinsed in water. This method recognizes that alkali metals tend to bind tenaciously to oxides and that the alkali metals will be within a few Angstrom of the surface of the device surface. Thus, by etching a thin layer of the contaminated surface, the contaminating alkali metals will be etched, rendered water soluble and washed away. However, during such down stream halogen-based (e.g., fluorine) plasma etching the device is subjected to a large amount of reactive halogen-species, e.g., fluorine-species. Such halogen-species may react with the oxide surface and may also become trapped in the pores and cavities of the surface being etched as labile halogen (e.g., labile fluorine). Moreover, subsequent water and/or solvent rinse results in corroded vias or metal connections due to the solvated, labile halogen acting as an electrolyte. Therefore, although the alkali metal contaminants may be sufficiently removed, the process introduces additional contaminants to the device.